Edge connectors for printed circuit boards are well known and widely used as the principle means of interconnecting electronic subassemblies which form functioning devices such as computers, telecommunications gear, test apparatus and the like. Such connectors are often termed "PC board connectors" or edge card connectors and are typically comprised of plastic material formed into what is known as a housing and made to contain a series of electrical contacts stamped and formed and plated to interconnect the individual components on a daughter board through pads on the edge thereof to circuits in or on a mother board via tabs or posts soldered thereto. The contacts of the connector generally are arranged to have spring portions which allow the daughter boards to be plugged in or removed therefrom. This arrangement permits replacement, repair or changes in components on the daughter boards to be done apart from the location of the mother board. It further allows the different circuits and arrangements of components to be individually packaged so as to be separately processible in production.
The concept of the use of printed circuit boards to mount components as on daughter boards and to be pluggably interconnected as on mother boards has indeed become one of the major means of providing electronic circuits of all kinds, and the connectors used therefor are widely employed in industry. U.S. Pat. No. 4,077,694 shows an example of an edge card connector which has two rows of terminals which contact both sides of a daughter board, and U.S. Pat. No. 3,601,775 shows a similar arrangement for contact of one side of a board.
In general, the printed circuit board connector serves a first function of allowing the mounting of contacts on appropriate centers in an appropriate orientation to make contact with pads on daughter boards on the one hand, and contact with pads or holes in a mother board interconnected to circuits thereon. A second function performed by the connector is to physically mount the daughter board in a stable and reliable manner so that it will not be unintentionally displaced or disturbed in use. It is particularly critical that the daughter board not be allowed to move through vibration or other physical stimuli relative to the electrical interface with the connector contact, as this can cause circuit intermittence as well as a deterioration of the contact interfaces due to fretting corrosion or the like. The connector housing which is typically of a dielectric material suitably moldable, contains card or board guides so as to accurately position a daughter board relative to a mother board so that all interconnections are maintained properly in both a physical and dimensional sense and in terms of suitable electrical isolation.
As a general rule, card guides or other such structures are employed to help align daughter boards during insertion into printed circuit board connectors and more importantly, to support such boards so that the weight thereof will not overly stress the contacts contained in such connectors or the housings of the connectors, particularly with respect to the weight of the components mounted on daughter boards. This weight is not always static in that electronic packages are frequently subjected to movement in a variety of attitudes, vibration, shock as by dropping, or sudden changes in velocity or acceleration; all expressed in at least some part in a variety of compressional, sheer and tensional forces on the connector housing, as well as on the contacts therein.
The advance of semiconductor technology has resulted in development of chip carriers which comprise substrates on which the chips are mounted and electrically connected by fine wires. The substrates are plugged into sockets having resilient contact members which make contact with surface traces on the substrate. See, e.g., U.S. Pat. No. 3,753,211, which discloses a socket having terminals for contact with opposed edges. In some applications, as where as board space is at a premium, it is desirable to connect the substrate edge to the board. One such application is the use of edge mounted memory modules in the form of single in-line memory modules. Standard card edge connectors cannot be simply downsized to meet the requirements of a substrate to board connection, known as a level two connection. This connection is relatively much smaller and requires simple, compact contacts on a much smaller spacing. As such, variations in board thickness and board warpage are much more likely to deflect contact means beyond the elastic limit, which would adversely affect contact pressure and thus the integrity of the electrical connection of future substrate insertions.
Given that the single in-line memory modules have a tendency for the boards to warp, the housing which carries the electrical contacts must be designed to optimally resist the warpage of the housing also. Furthermore with the anticipated vibration of the connectors and modules, it is important that the connector to include a latching means to detect the full insertion of the module into the socket and to prevent the withdrawal of the module during vibration. Further considerations to the design of the connector relate to the attempt to increasing requirement of optimizing the real estate usage of the board while maintaining a small envelope and low profile in which the assembly resides.